| Summary: | 碩士 === 輔仁大學 === 食品營養學系 === 89 === Lycopene is an important biological carotenoid that is widely distributed in fruits and vegetables. Epidemiological study has shown that the dietary intake of lycopene may reduce the risk of certain types of cancers such as prostate cancer. However, the formation of cis-isomers of lycopene during food processing and storage may decrease its biological activity. Thus, it is important to separate, identity and quantity lycopene and its cis isomers. In this study we compared two types of columns (C18 and C30) and various solvent systems for the separation of lycopene and its cis isomers by HPLC, as well as identification by spectra analyses. The stability of lycopene and its cis isomers during illumination and heating was also studied. Results showed that all-trans-lycopene and its nine cis isomers could be resolved by employing a C30 column with a mobile phase of n-butanol-acetonitrile-methylene chloride (30:70:10, v/v/v) and flow rate 2 mL/min within 35 min. A C30 column was found to provide a more powerful resolution for lycopene and its cis isomers, however, the retention time was drastically increased when compared to a C18 column. Lycopene cis-isomers were tentatively identified as 5-cis, 9-cis, 13-cis and 15-cis-lycopene, and possibly four lycopene di-cis isomers and another mono-cis isomer, based on spectral characteristics and Q ratios as reported in the literature. The degradation of total amount of lycopene and its cis isomers during illumination at 2000~3000 Lux (25℃) fits a first-order model. Also, both 13-cis-lycopene and 15-cis-lycopene were the major isomers formed during illumination. During heating at 50℃ in the first nine hours, the isomerization reaction dominated. However, the degradation was the major reaction afterwards. At 100 and 150℃, the degradation reaction was more pronounced than the isomerization reaction. The degradation rate constant of lycopene rose with increasing temperature, and the activation energy was calculated to be 61.0 KJ/mol.
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